Well I wouldn't call him the "forgotten" inventor as he did get some credit for lots of things. It's true though that some of his inventions were more or less "stolen" with him actually being the first one to invent them...

There also are some rumors about some of his inventions where we don't really have lots of details on. It ranges from "free energy devices" (but I don't know if there actually exist hints on actual designs or if it's just about some ideas of his) to things not really understood because of a lack of details (which he didn't give because he feared it would be stolen again). I for example remember that he had a design for something which pretty much were some foils or anything like that put on the top of a pole and he claimed to be able to get electrical power by putting that pole at quite a height and if I remember correctly it was about light or radiation his device could convert. But as said it was like the request for a patent where he left out any details so no one would steal the idea...

He definitely was a great inventor but also one of the poor guys of history who got used by others and didn't get the credit they deserved. I think to this day even school books didn't change the actual inventor to his favor although we now know that he was first with certain things...